I have a white jacket... Well, not pure white (check my avatar) and I haven't had any problems with it getting dirty. Nothing that a quick wet rub didn't get off.
I don't jib though so maybe it gets dirty from failed jibs? I could totally see it getting dirty in trees and backcountry though. Not that I would even recommend a white jacket for the latter two types of riding though (you don't want to be invisible if you get lost in some trees or in the backcountry).
In the Gunmetal
686 Mannual Source Mens Shell Snowboard Jacket 2011
Black or Marine
Bonfire Baker Mens Shell Snowboard Jacket 2011
Acid or Black
686 Reserved Volt Mens Shell Snowboard Jacket 2011
Natural Loom or Bluebird
Foursquare Coco Mens Insulated Snowboard Jacket 2011
Volcom Blast Mens Insulated Snowboard Jacket 2011